feat: add option to disable update checker

Add a new setting in User Profile > Settings to disable automatic
update checking on startup and dashboard.

- Adds 'Disable Update Check' toggle in profile settings
- Skips GitHub API calls when disabled (reduces network requests)
- Works for both web app and Electron client

Fixes Termix-SSH/Support#410

src/ui/desktop/user/ElectronVersionCheck.tsx

@@ -30,6 +30,11 @@ export function ElectronVersionCheck({
   const lineColor = isDarkMode ? "#151517" : "#f9f9f9";
 
   useEffect(() => {
+    const updateCheckDisabled = localStorage.getItem("disableUpdateCheck") === "true";
+    if (updateCheckDisabled) {
+      onContinue();
+      return;
+    }
     if (isElectron()) {
       checkForUpdates();
     } else {